1. Field of the Invention
The present invention relates to an apparatus for controlling an electric motor and an apparatus for controlling a hybrid vehicle.
2. Description of the Related Art
Electric vehicles and hybrid vehicles which incorporate electric motors for generating propulsive forces for the vehicles operate selectively in power and regenerative modes for the electric motors depending on the operating state (the accelerator pedal operation, the vehicle speed, etc.) of the vehicles. Generally, a torque command value (a command value of the power torque or regenerative torque) for the electric motor is generated depending on the operating state of the vehicle, and an output torque of the electric motor is controlled depending on the generated torque command value. Various control processes including a so-called d-q vector control process are known in the art for controlling the output torque of the electric motor depending on the torque command value.
Electric motors mounted on electric vehicles and hybrid vehicles are required to produce a wide range of output torques in view of their application, and are often needed to produce an output torque in excess of the rated torque at which the electric motors are capable of continuous operation without fail. Therefore, the electric motors are frequently operated while generating a relatively large amount of heat with a large current passing therethrough, and hence are required to prevent themselves from being overheated. According to a known solution, as disclosed in Japanese laid-open patent publications Nos. 11-27806 and 2000-32602, the temperature of an electric motor is detected by a temperature sensor, and when the detected temperature exceeds a predetermined temperature, the output torque of the electric motor is forcibly limited.
However, the conventional arrangement which uses the temperature sensor to detect the temperature of an electric motor is highly costly because it requires the temperature sensor itself and parts by which the temperature sensor is installed on the electric motor. Furthermore, a plurality of temperature sensors need to be actually used for continued operation in the event of a temperature sensor failure. As a result, the cost of the entire system is higher, and it is hard to keep an installation space for the temperature sensors.
It is therefore an object of the present invention to provide an apparatus for controlling an electric motor to prevent the electric motor from being overheated with an inexpensive simple means without the need for temperature sensors.
Another object of the present invention to provide an apparatus for controlling a hybrid vehicle to prevent an electric motor in the hybrid vehicle from being overheated with an inexpensive simple means.
The inventors have found that while an electric motor is operating with a normal output torque, e.g., an output torque smaller than a rated torque, the temperature of the electric motor generally does not become excessively high, and the steady temperature of the electric motor during such an operating state is substantially constant. For preventing the electric motor from being overheated, it is considered sufficient to be able to recognize temperature changes of the electric motor basically in a situation where the output torque of the electric motor is relatively large.
A temperature change of the electric motor within a sufficiently short period of time (an instantaneous temperature change), or particularly a temperature change upon a temperature increase from the steady temperature of the electric motor, can be inferred using data of a torque command value for the electric motor and data of an average of torque command values. Since a current flowing through the armature of the electric motor is basically proportional to the torque command value, the torque command value is closely related to the amount of heat (Joule heat) generated by the electric motor which is mainly responsible for the temperature increase of the electric motor. The average of torque command values is closely related to the tendency of the temperature change of the electric motor (the tendency for the temperature change of the electric motor to increase or decrease). Therefore, it is possible to appropriately infer the temperature change of the electric motor using the data of the torque command value and the data of the average of torque command values.
To achieve the above objects, there is provided in accordance with the present invention an apparatus for controlling an electric motor depending on a torque command value, comprising inference means for sequentially calculating an inferred value of a temperature change of the electric motor in each cycle time using at least data representing the torque command value and data representing an average of torque command values, integrating means for sequentially integrating the inferred value of the temperature change of the electric motor to calculate an accumulated temperature change, and output limiting means for limiting the output of the electric motor when the accumulated temperature change exceeds a predetermined output limiting threshold.
According to the present invention, there is also provided an apparatus for controlling a hybrid vehicle having an engine for generating a propulsive force for the hybrid vehicle, an electric motor coupled to an output shaft of the engine for selectively generating an assistive propulsive force for the hybrid vehicle in a power mode and generating electric energy using the kinetic energy of the hybrid vehicle as an energy source in a regenerative mode, depending on the operating state of the hybrid vehicle, and an electric energy storage device as a power supply for the electric motor in the power mode, the arrangement being such that a torque command value for the electric motor is generated depending on the operating state of the hybrid vehicle, and the electric motor is controlled depending on the torque command value, the apparatus having the inference means, the integrating means, and the output limiting means described above in the apparatus for controlling the electric motor.
With the apparatus for controlling the electric motor and the apparatus for controlling the hybrid vehicle according to the present invention, using at least the data representing the torque command value and the data representing the average of torque command values, it is possible to appropriately infer a temperature change of the electric motor in each cycle time. By integrating the inferred value of the temperature change with the integrating means, an accumulated temperature change from an arbitrary temperature of the electric motor can sequentially be recognized. When the accumulated temperature change exceeds the output limiting threshold, the output of the electric motor is limited by the output limiting means thereby to prevent the electric motor from being overheated. The accumulated temperature change can be determined by a processing operation of a microcomputer or the like without the need for sensors such as temperature sensors.
According to the present invention, therefore, the electric motor is prevented from being overheated with an inexpensive arrangement without the need for sensors such as temperature sensors.
With the apparatus for controlling the electric motor and the apparatus for controlling the hybrid vehicle according to the present invention, various algorithms may be employed to determine the inferred value of the temperature change. For example, the inference means may comprise fuzzy inference means for sequentially calculating an inferred value of a temperature change of the electric motor according to a fuzzy inference operation using at least the data representing the torque command value and the data representing an average of torque command values as input parameters.
According to the inventors"" finding, when the data representing the torque command value and the data representing the average of torque command values as input parameters of the fuzzy inference operation, it is possible to appropriately infer, with relatively high accuracy, a temperature change of the electric motor according to the fuzzy inference operation by suitably establishing a fuzzy inference algorithm (specifically membership functions and fuzzy rules). Consequently, it is possible to appropriately prevent the electric motor from being overheated.
With the inference means comprising the fuzzy inference means, membership functions and fuzzy rules used in the fuzzy inference operation are established such that the inferred value of the temperature change is substantially zero when the torque command value is present in a predetermined range.
With the above arrangement, it is possible to keep the accumulated temperature change at a value close to xe2x80x9c0xe2x80x9d in a steady temperature of the electric motor when the electric motor is operated by controlling the output torque of the electric motor at a normal torque. The accumulated temperature change determined when the output torque of the electric motor is relatively large represents a temperature change from the steady temperature of the electric motor. As a consequence, the output of the electric motor can be limited at a suitable time depending on the accumulated temperature change.
The fuzzy inference means preferably comprises means for using a first membership function for classifying and expressing the degree of the magnitude of the torque command value, a second membership function for classifying and expressing the degree of the magnitude of the average of torque command values, and a plurality of fuzzy rules having the input parameters in an antecedent part thereof and a plurality of preset values for the temperature change in a consequent part thereof, determining the fitnesses of the input parameters with respect to the antecedent part of the fuzzy rules based on the first and second membership functions, and determining the center of gravity of the temperature change in the consequent part as the inferred value of the temperature change using the determined fitnesses as weighting coefficients.
The fuzzy inference means can thus calculate the inferred value of the temperature change according to a relatively simple process.
Since the torque command value is closely related to the amount of heat (Joule heat) generated by the electric motor and the average of torque command values is closely related to the tendency of the temperature change of the electric motor, the first membership function is preferably established to represent a model of the amount of heat generated by the electric motor with respect to the torque command value, and the second membership function is preferably established to represent a model of the tendency of the temperature change of the electric motor with respect to the average of torque command values.
Specifically, because the amount of heat (Joule heat) generated by the electric motor is basically proportional to the square of the torque command value, the first membership function relative to the torque command value is preferably established to classify the magnitude of the torque command value into three degrees, i.e., xe2x80x9csmallxe2x80x9d, xe2x80x9cmediumxe2x80x9d, and xe2x80x9clargexe2x80x9d, for example. For preventing the electric motor from being overheated, a temperature increase from the steady temperature of the electric motor poses a problem. Therefore, a range of torque command values for preventing the temperature of the electric motor from increasing from the steady temperature (e.g., a range of torque command values below the rated torque of the electric motor) is preferably classified as xe2x80x9csmallxe2x80x9d, and ranges of torque command values for allowing the temperature of the electric motor to increase from the steady temperature are preferably classified as xe2x80x9cmediumxe2x80x9d and xe2x80x9clargexe2x80x9d.
The second membership function relative to the average of torque command values is preferably representative of a state in which the temperature of the electric motor has a tendency to increase from the steady temperature and a state in which the temperature of the electric motor has a tendency to decrease from the steady temperature. The second membership function is preferably established to classify the magnitude of the average of torque command values into two degrees, i.e., xe2x80x9csmallxe2x80x9d and xe2x80x9clargexe2x80x9d, for example. Therefore, a range of averages of torque command values for allowing the temperature of the electric motor to increase from the steady temperature (e.g., a range of torque command values above the rated torque of the electric motor) is preferably classified as xe2x80x9clargexe2x80x9d, and a range of averages of torque command values for allowing the temperature of the electric motor to decrease from the steady temperature (e.g., a range of torque command values sufficiently smaller than the rated torque of the electric motor) is preferably classified as xe2x80x9csmallxe2x80x9d.
If the apparatus has an electric energy storage device as a power supply for the electric motor, the apparatus should preferably further comprise consequent part correcting means for correcting at least one of the preset values for the temperature change in the consequent part of the fuzzy rules depending on the temperature of the electric energy storage device.
With the above arrangement, it is possible to adjust, depending on the temperature of the electric energy storage device, the magnitude of the inferred value of the temperature change calculated by the fuzzy inference means and hence the value of the accumulated temperature change calculated by the integrating means. Consequently, the output of the electric motor can be limited in view of the temperature of the electric energy storage device as the power supply for the electric motor.
Specifically, the consequent part correcting means preferably comprises means for correcting at least one of the preset values for the temperature change in order to reduce the inferred value of the temperature change as the temperature of the electric energy storage device is lower, and to increase the inferred value of the temperature change as the temperature of the electric energy storage device is higher.
By thus correcting at least one of the preset values for the temperature change in the consequent part of the fuzzy rules of the fuzzy inference means depending on the temperature of the electric energy storage device, when the temperature of the electric energy storage device is relatively low, even if the torque command value is relatively large, the rate at which the accumulated temperature change increases is reduced, the output of the electric motor is limited later than when the temperature of the electric energy storage device is normal. The period in which a relatively large current flows through the electric energy storage device is increased, making it possible to warm up the electric energy storage device quickly and preventing the electric energy storage device from suffering a reduction in its electric energy supplying capability in a low temperature environment such as during winder. When the temperature of the electric energy storage device is low, the temperature of the electric motor is also relatively low. Therefore, even if the output of the electric motor is limited later than when the temperature of the electric energy storage device is normal, no problem arises in preventing the electric motor from being overheated.
Conversely, when the temperature of the electric energy storage device is relatively high, the rate at which the accumulated temperature change increases is increased if the torque command value is relatively large, and hence the output of the electric motor is limited earlier than when the temperature of the electric energy storage device is normal. Consequently, the electric motor is reliably prevented from being overheated, and the temperature of the electric energy storage device is simultaneously prevented from being excessively increased.
Therefore, the electric energy storage device can be kept at a desired temperature, and can maintain its desired charging and discharging performance.
The output limiting means preferably comprises means for limiting the output torque of the electric motor to a torque which is equal to or lower than a predetermined torque which is preset to lower the temperature of the electric motor. This arrangement is effective in reliably preventing the electric motor from being overheated.
The output limiting means preferably comprises means for canceling the limitation of the output of the electric motor when the accumulated temperature change exceeds the output limiting threshold and thereafter becomes lower than a predetermined limitation canceling threshold which is smaller than the output limiting threshold.
With the above arrangement, when the accumulated temperature change exceeds the output limiting threshold and the output limiting means starts limiting the output of the electric motor, the output of the electric motor is continuously limited until the accumulated temperature change becomes lower than the limitation canceling threshold which is lower than the output limiting threshold. Thus, the limitation of the output of the electric motor has hysteresis characteristics with respect to the accumulated temperature change. As a consequence, the process of limiting the output of the electric motor and the process of canceling the limitation of the output of the electric motor are prevented from being frequently carried at short time intervals, preventing the output torque of the electric motor from fluctuating frequently.
A so-called d-q vector control process is generally known for controlling an electric motor such as a DC brushless motor. In the d-q vector control process, a d-q coordinate system is assumed which has a d-axis representing the direction of a magnetic field of the electric motor and a q-axis representing the direction perpendicular to the direction of the magnetic field, and the armature circuit of the electric motor is represented by an equivalent circuit comprising a hypothetical armature in the d-axis direction and a hypothetical armature in the q-axis direction. An armature current component id in the d-axis direction and an armature current component iq in the q-axis direction are determined depending on the torque command value, and the armature current (phase current) of the electric motor is vector-controlled based on the determined armature current components id, iq. If the direction of the magnetic field of the electric motor is the d-axis direction, then the armature current component id has a function as an exciting current and the armature current component iq has a function as a current for determining the output torque of the electric motor.
In the d-q vector control process, a field weakening control process is performed in a range of high rotational speeds of the electric motor. In the field weakening control process, the armature current (phase current) of the electric motor is relatively large even if the output torque of the electric motor is relatively small. More specifically, in the field weakening control process, the armature current (phase current) of the electric motor is represented by (id2+iq2). Therefore, the torque command value (xe2x88x9diq) is not proportional to the armature current of the electric motor in the field weakening control process. The field weakening control process is not carried out in the d-q vector control process in a range of low rotational speeds of the electric motor. When id≈0, the armature current of the electric motor is approximately equal to the armature current component iq in the q-axis direction, and the torque command value is proportional to the armature current of the electric motor.
If the apparatus has means for performing a d-q vector control process of the electric motor, as means for controlling the electric motor depending on the torque command value, then the apparatus comprises torque command correcting means for correcting the torque command value depending on at least a rotational speed of the electric motor, and the fuzzy inference means is supplied with a corrected value of the torque command value produced by the torque command correcting means and an average of corrected values produced by the torque command correcting means, as the input parameters, rather than the torque command value and the average of torque command values.
More specifically, the torque command correcting means comprises means for correcting the torque command value so as to be increased as the rotational speed of the electric motor is higher.
With the above arrangement, when the rotational speed of the electric motor is high and the field weakening control process is performed, the corrected value representing the torque command value corrected so as to be increased and an average of corrected values are supplied as input parameters to the fuzzy inference means. Therefore, input parameters having a magnitude based on the actual armature current of the electric motor are supplied to the fuzzy inference means. As a result, even when the field weakening control process is being carried out, the inferred value of a temperature increase of the electric motor per cycle time can appropriately be calculated, and hence the accumulated temperature change can appropriately be obtained. Accordingly, the electric motor is appropriately prevented from being overheated.
In the d-q vector control process, the relationship between the torque command value and the actual armature current of the electric motor is slightly affected by the power supply voltage (the voltage of the electric energy storage device) of the electric motor. Therefore, the torque command value may be corrected by the torque command correcting means depending on not only the rotational speed of the electric motor, but also the power supply voltage of the electric motor. Since the actual armature current of the electric motor with respect to the torque command value is greater as the power supply voltage of the electric motor is higher, the torque command value should preferably be corrected so as to be increased as the power supply voltage is lower.
The various details described above of the apparatus for controlling the electric motor according to the present invention may be applied to the apparatus for controlling the hybrid vehicle according to the present invention. Particularly, if the fuzzy inference means comprises means for using a first membership function for classifying and expressing the degree of the magnitude of the torque command value, a second membership function for classifying and expressing the degree of the magnitude of the average of torque command values, and a plurality of fuzzy rules having the input parameters in an antecedent part thereof and a plurality of preset values for the temperature change in a consequent part thereof, determining the fitnesses of the input parameters with respect to the antecedent part of the fuzzy rules based on the first and second membership functions, and determining the center of gravity of the temperature change in the consequent part as the inferred value of the temperature change using the determined fitnesses as weighting coefficients, then the apparatus preferably further comprises consequent part correcting means for correcting at least one of the preset values for the temperature change in the consequent part of the fuzzy rules depending on the engine temperature of the engine.
With the above arrangement, it is possible to adjust, depending on the engine temperature of the engine, the magnitude of the inferred value of the temperature change which is calculated by the fuzzy inference means based on the torque command value and its average value, and hence the value of the accumulated temperature change calculated by the integrating means. Thus, the output of the electric motor can be limited in view of the temperature of the engine.
Specifically, the consequent part correcting means preferably comprises means for correcting at least one of the preset values for the temperature change in order to reduce the inferred value of the temperature change by a smaller value when at least the engine temperature of the engine is lower than a predetermined temperature than when the engine temperature is higher than the predetermined temperature.
By thus correcting at least one of the preset values for the temperature change in the consequent part of the fuzzy rules of the fuzzy inference means depending on the engine temperature of the engine, when the engine temperature is low and hence the engine is cold, even if the torque command value is relatively large, the rate at which the accumulated temperature change increases is reduced, and the output of the electric motor is limited later than when the temperature of the electric energy storage device is normal. Therefore, it is possible to appropriately maintain a drive power required by the vehicle while suppressing the load on the engine at a low temperature, making it possible for the vehicle to exhibit a good running performance. When the engine temperature is low, the temperature of the electric motor is also relatively low. However, since there is a more chance for a relatively large current to flow through the electric motor, the electric motor can be warmed up early. Because when the engine temperature is low, the temperature of the electric motor is also relatively low, no problem arises in preventing the electric motor from being overheated even if the output of the electric motor is limited later than when the engine temperature is normal.
If the apparatus has engine loss reduction control means for performing a process of reducing a pumping loss of the engine when the electric motor operates in the regenerative mode, then the apparatus preferably comprises engine loss reduction inhibiting means for inhibiting the process of reducing a pumping loss of the engine from being performed by the engine loss reduction control means when the accumulated temperature change exceeds a predetermined engine loss reduction inhibiting threshold which is lower than the output limiting threshold.
If the accumulated temperature change increases in the regenerative mode of the electric motor and the output of the electric motor is to be limited, then the process of reducing a pumping loss of the engine is inhibited before the output of the electric motor starts to be limited. Therefore, when the output of the electric motor starts to be limited, so-called engine braking is applied to the hybrid vehicle. As a result, even if the braking power of the vehicle produced by the regenerative mode of the electric motor is abruptly reduced by the limitation of the output of the electric motor, engine braking is applied in a manner to compensate for the reduction of the braking power, resulting in a desired amount of braking power for braking the vehicle.
The process of reducing a pumping loss of the engine is performed by stopping the supply of the fuel to at least one cylinder of the engine and closing the intake and exhaust valves of the cylinder, or opening a valve mounted on an exhaust gas recirculation path which connects the exhaust passage to intake passage of the engine, or delaying the closing or opening of the intake and exhaust valves of the cylinder.
If the process of reducing a pumping loss of the engine is to be inhibited, then the engine loss reduction inhibiting means preferably comprises means for permitting the process of reducing a pumping loss of the engine to be performed by the engine loss reduction control means when the accumulated temperature change exceeds the engine loss reduction inhibiting threshold and thereafter becomes lower than a predetermined engine loss reduction permitting threshold which is lower than the engine loss reduction inhibiting threshold.
With above arrangement, when the accumulated temperature change exceeds the engine loss reduction inhibiting threshold, and the process of reducing a pumping loss of the engine to be performed by the engine loss reduction control means is inhibited, the inhibition continues until the accumulated temperature change becomes lower than the engine loss reduction permitting threshold which is lower than the engine loss reduction inhibiting threshold. Therefore, the processes of inhibiting and permitting the reduction of a pumping loss of the engine are carried out with hysteresis characteristics with respect to the accumulated temperature change. As a result, the inhibition or permission of the reduction of a pumping loss of the engine is prevented from being frequently carried out at short time intervals, allowing the vehicle to run smoothly.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.